With the exponential growth of a service volume of a user, a radio resource has gradually become an extremely scarce resource, and to provide a higher data rate by further improving the spectrum efficiency on a limited spectrum resource has become an urgent problem to be solved in wireless communications.
Currently, a highest-order modulation mode supported by a long terminal evolution (LTE) system in 3GPP is 64 quadrature amplitude modulation (QAM). In order to further improve the spectrum efficiency, the LTE system needs to support a higher-order modulation mode such as 256QAM and 1024QAM, and especially, in a scenario of small indoor coverage, the channel quality is good, and a user may obtain a high signal-to-noise ratio, which provides feasibility for an application of the modulation mode such as 256QAM and 1024QAM. The performance of the modulation mode such as 256QAM and 1024QAM relies on an error vector magnitude (EVM) index of a transmit signal, and the lower the EVM is, the better the demodulation performance at a receiving end becomes.
Currently, in the LTE system, downlink data is sent by using an orthogonal frequency division multiplexing (OFDM) modulation mode, a peak average power rate (PAPR) of a signal obtained through modulation by the OFDM is high, and an EVM index that can be reached is also high, which is not suitable for supporting the high-order modulation mode such as 256QAM 1024QAM; therefore, the improvement of the data rate is limited. In addition, when the downlink data is sent by using the OFDM modulation mode, a cell edge user cannot be effectively served.